Construction machines such as hydraulic excavators include those constructed such that a swing frame and an upperstructure, which is arranged on the swing frame and is composed of various devices, can be caused to swing relative to a base such as an undercarriage. The term “swing mechanism for a construction machine” means a mechanism constructed by arranging a swing frame, an inner annular ring having an internal gear on an inner circumferential portion thereof and mounted on a side of a base, an outer annular ring rotatably arranged surrounding the inner race and provided with the swing frame secured thereon by bolts, a pinion maintained in meshing engagement with the internal gear of the inner race, and a pinion drive device for rotationally driving the pinion such that such an upperstructure is allowed to achieve a swing motion. This pinion drive device serves as a drive source for causing the upperstructure to swing relative to the base, and in general, is equipped with a motor such as a hydraulic motor and a reduction gear box for transmitting rotation of the motor at a reduced speed to a pinion and is arranged on the side of the swing frame.
A swing mechanism for a construction machine is designed such that a pinion on the side of a swing frame is brought into meshing engagement with an internal gear of an inner race on the side of an undercarriage to permit swinging of the swing frame, which forms an upperstructure, relative to a base. It is, therefore, necessary to maintain the pinion and the inner gear in adequate meshing engagement so that the upperstructure does not shake upon swinging. When plural hydraulic excavators are assembled, however, a backlash formed at a place of meshing engagement between a rotating pinion and a ring gear on an inner race of a swing circle in each swing mechanism substantially varies from one swing mechanism to another, resulting in a problem that the hydraulic excavators tend to be reduced in quality.
To cope with such a problem, an invention disclosed, for example, in Patent Publication 1 has been proposed. In a mounting structure for a swing unit that the mounting structure is arranged on a construction machine equipped with a traveling unit and the swing unit arranged on the traveling unit via a swing circle having an inner race and outer race, the swing unit having a rotational pinion is secured by bolts on a main frame of the swing unit, the outer race of the swing circle is secured by bolts on the main frame of the swing unit, the inner race of the swing circle is secured by bolts on the traveling unit, and the swing unit is arranged to maintain the inner race of the swing circle in meshing engagement with a ring gear of the inner race of the swing circle, the invention is characterized in that at least one of a single pin for the swing unit, said single pin connecting the swing unit to the main frame, and a single pin for the swing circle, said pin connecting the outer race of the swing circle to the main frame, is arranged and at least one of a pin for the swing unit and a pin for the swing circle is arranged on a center connecting line, which connects a center of the above-described swing circle and a center of the swing unit with each other, or in the vicinity of the center connecting line.
Patent Publication 1: JP-A-2000-336696 (pages 3-5, FIGS. 1-2).